Images, as well as video streams, direct from image sensors are usually provided in one of several formats. These formats include Compact Camera Port (CCP), CCP Joint Photographic Experts Group (JPEG), International Telecommunications Union (ITU) and ITU JPEG. An image frame that is output from an image sensor in one of these formats contains additional information beyond that of simply the data of the image.
For example, referring to FIG. 1, a typical CCP formatted frame 10 is shown. The frame 10 begins with a start of frame data SOF indicating to any serial reader of the frame where the first line of the frame begins. The first line is then followed by end of line data EOL so the serial reader now knows that it has the first line of the frame. Following the end of line data EOL, checksum data is provided to verify the integrity of the image data contained in the first line. Following the checksum data is a blank period separating the data associated with the first line to that of the second. This data area is known as the line blanking period. Start of line data SOL then indicates the beginning of a second line of data. This is then followed by the image data, the end of line data EOL, a checksum and then the line blanking period. The same order continues for each line until the last line, which instead of the end of line data EOL has the end of frame data EOF.
Following the last line, including its line blanking period, is another blank period separating the current frame from the next one, which is known as the frame blanking period. Blanking periods are introduced into image frames from an image sensor to allow for image scaling. The blank period provides a buffer for timing and scaling, and for delays in electronics in the image sensor or coprocessor to allow time for the electronics to colorize the image (raw outputs from an image sensor are bayer images).
When image streams are received by a computer over a communication link, such as a USB2 (Universal Serial Bus 2) communication link, in one of these formats at least two problems effect the quality of the video image stream displayed. First, insufficient bandwidth is available in a USB2 communication link to transmit all image frames at the rate at which the sensor is capable (for a relatively high resolution image sensor, such as one having 1600×1200 pixels), which is typically 30 frames per second. As such, the image sensor has to be de-rated by reducing the output frame rate so that all produced images can be received.
As a result of the slower frame rate, motion blur occurs in the displayed video, and therefore, does not represent the quality of the image stream that can be produced. Second, when images are transmitted in one of these formats over a communication channel, such as a USB2 link, the software in the receiving system is required to manipulate the image data for removing the portions which are not required for display. This operation further limits the frame rate at which images can be displayed on the receiving system.